Adsorption, absorption and biological degradation of ammonia in different biofilter organic media

A tailor-made apparatus called ammoniometer, which is a batch mode respirometer applied to the study of ammonia biodegradation in biofilter media, has been used to evaluate adsorption, absorption, and biodegradation in five different organic materials (compost, coconut fibre, bark, pruning wastes, and peat) obtained from full-scale biofilters in operation in several waste treatment plants. The results showed that absorption could be represented by a Henry's law linear equation, with values of the Henry coefficient significantly higher (from 1,866 to 15,320) than that of pure water (1,498). Adsorption data were successfully fitted to Langmuir and Freundlich isotherms and maximum adsorption capacity varies from 1.06 to 1.81 mg NH(3)/g dry media. Ammonia biodegradation rates for each organic material were also calculated. Biodegradation rates varied from 0.67 to 7.82 mg NH(3)/kg media/d depending on the material tested. The data obtained showed important differences in the behaviour of the biofilter organic media, which has important implications in the design and modelling of these systems

Composting of dewatered wastewater sludge with various ratios of pruning waste used as a bulking agent and monitored by respirometer

The effects of different volumetric ratios of wastewater sludge to bulking agent on the performance of full-scale composting were studied. Volumetric ratios of wastewater sludge to pruning waste, used as a bulking agent, were 1:2 (Pile 1), 1:2.5 (Pile 2) and 1:3 (Pile 3). Experiments were carried out in an uncovered plant using windrow composting with weekly turning. To monitor the evolution of the three composting piles, routine parameters such as temperature and interstitial oxygen level, chemical parameters such as organic matter, moisture and C/N ratio, and biologically related indices such as respiration indices at process temperature (RIprocess) and at 37 °C (RI₃₇) were monitored. Different responses were observed in the three piles; Pile 1 did not accomplish the necessary requirements in terms of sanitation and RIprocess for a typical composting process; Piles 2 and 3 presented a similar behaviour, reaching thermophilic temperatures for a long period and, due to their high biological activity, high RIprocess. The quality of the product obtained in the three piles in terms of stability (RI₃₇ and the Rottegrade self-heating test) and maturity (germination index) were measured, with compost from Pile 3 the most stable. To achieve satisfactory stability and sanitation for application to land, optimisation of the sludge to bulking agent ratio used to process wastewater sludge into compost appears to be crucial

Emission of volatile organic compounds from composting of different solid wastes : abatement by biofiltration

Emission of volatile organic compounds (VOCs) produced during composting of different organic wastes (source-selected organic fraction of municipal solid wastes (OFMSW), raw sludge (RS) and anaerobically digested wastewater sludge (ADS) and animal by-products (AP)) and its subsequent biofiltration have been studied. Composting was performed in a laboratory scale composting plant (30 l) and the exhaust gases generated were treated by means of a compost biofilter. VOCs concentration in the composting exhaust gases for each composting process ranged from 50 to 695 mg C m⁻³ for OFMSW (5:1), from 13 to 190 mg C m⁻³ for OFMSW (1:1), from 200 to 965 mg C m⁻³ for RS, from 43 to 2900 mg C m⁻³ for ADS and from 50 to 465 mg C m⁻³ for AP. VOCs emissions were higher during the beginning of the composting process and were not generally related to the biological activity of the process. These emissions corresponded to an average loading rate applied to the biofilter from 2.56 to 29.7 g C m⁻³ biofilter h⁻¹. VOCs concentration in the exhaust gas from the biofilter ranged from 55 to 295 mg C m⁻³ for OFMSW (5:1), from 12 to 145 mg C m−3 for OFMSW (1:1), from 55 to 270 mg C m−3 for RS, from 42 to 855 mg C m⁻³ for ADS and from 55 to 315 mg C m⁻³ for AP. Removal efficiencies up to 97% were achieved although they were highly dependent of the composted waste. An important observation was that the compost biofilter emitted VOCs with an estimated concentration of 50 mg C m⁻³

Coupling composting and biofiltration for ammonia and volatile organic compounds removal

The efficiency of a compost biofilter for the simultaneous removal of ammonia and volatile organic compounds (VOCs) from exhaust gases of the composting process of different organic wastes (source-selected organic fraction of municipal solid wastes and animal by-products) is studied. An average ammonia removal efficiency of 94.7% was obtained in the biofilter for an average loading rate range of 846-to 67100 mg [NH3] m⁻³ biofilter h⁻¹. However, a sharp reduction in NH3 removal was observed when the waste gas contained a high, more than 2000 mg m⁻³, NH3 concentration. The maximum VOC removal efficiency was 82% when the biofilter worked at a loading rate range of 0.55-28.8 g [C] m⁻³ biofilter h⁻¹

Biofiltration for ammonia removal from composting exhaust gases

A study was conducted to investigate the utilization of mature compost as a biofilter media for the removal of ammonia from the exhaust gases of the composting process. Source-selected organic fraction of municipal solid wastes, digested wastewater sludge and animal by-products were composted in a pilot-scale reactor and the exhaust gas was treated in a biofilter. Due to the high ammonia adsorption and absorption capacity of the compost media, no delay or start-up phase was observed and high removal efficiencies were achieved from the beginning of the experiments. A global ammonia removal efficiency of 95.9% was obtained in the biofilter for a loading rate range of 846-67,100 mg NH₃ m⁻³ biofilter h⁻¹. However, an important reduction of ammonia removal was observed when the waste gas contained high NH₃ concentration (more than 2000 mg NH₃ m⁻³), which corresponded with the case of animal by-products composting

Composting of dewatered wastewater sludge with various ratios of pruning waste used as a bulking agent and monitored by respirometer

The effects of different volumetric ratios of wastewater sludge to bulking agent on the performance of full-scale composting were studied. Volumetric ratios of wastewater sludge to pruning waste, used as a bulking agent, were 1:2 (Pile 1), 1:2.5 (Pile 2) and 1:3 (Pile 3). Experiments were carried out in an uncovered plant using windrow composting with weekly turning. To monitor the evolution of the three composting piles, routine parameters such as temperature and interstitial oxygen level, chemical parameters such as organic matter, moisture and C/N ratio, and biologically related indices such as respiration indices at process temperature (RIprocess) and at 37 °C (RI₃₇) were monitored. Different responses were observed in the three piles; Pile 1 did not accomplish the necessary requirements in terms of sanitation and RIprocess for a typical composting process; Piles 2 and 3 presented a similar behaviour, reaching thermophilic temperatures for a long period and, due to their high biological activity, high RIprocess. The quality of the product obtained in the three piles in terms of stability (RI₃₇ and the Rottegrade self-heating test) and maturity (germination index) were measured, with compost from Pile 3 the most stable. To achieve satisfactory stability and sanitation for application to land, optimisation of the sludge to bulking agent ratio used to process wastewater sludge into compost appears to be crucial

Ammonia emissions from the composting of different organic wastes : dependency on process temperature

Ammonia emissions were quantified for the laboratory-scale composting of three typical organic wastes with medium nitrogen content: organic fraction of municipal solid wastes, raw sludge and anaerobically digested sludge; and the composting of two wastes with high nitrogen content: animal by-products from slaughterhouses and partially hydrolysed hair from the leather industry. All the wastes were mixed with the proper amount of bulking agent. Ammonia emitted in the composting of the five wastes investigated revealed a strong dependence on temperature, with a distinct pattern found in ammonia emissions for each waste in the thermophilic first stage of composting (exponential increase of ammonia emitted when increasing temperature) than that of the mesophilic final stage (linear increase of ammonia emissions when increasing temperature). As composting needs high temperatures to ensure the sanitisation of compost and ammonia emissions are one of the main environmental impacts associated to composting and responsible for obtaining compost with a low agronomical quality, it is proposed that sanitisation is conducted after the first stage in large-scale composting facilities by a proper temperature control

Full-scale co-composting of hair wastes from the leather manufacturing industry and sewage sludge

A full-scale cocomposting experiment using hair wastes from the leather manufacturing industry and sewage sludge as cosubstrates was carried out with the aim of producing compost that may be used as an organic amendment in agriculture. A 1:1 weight ratio of hair wastes and sewage sludge was used based on experiments at smaller-scale. The resulting mixture was then amended with pruning wastes acting as bulking agent in a 1:1 volumetric ratio (mixture:pruning wastes). The experiment was carried out using the windrow composting technology with a weekly turning frequency. Thermophilic range of temperature was quickly achieved and maintained for more than 8 weeks. This fact ensured the sanitation of the compost according to international requirements. Additionally, the quality of the product obtained expressed in stability terms was very high (Self-heating test grade: V; respiration index: 0.83 mg O₂ per gram of organic matter per hour). The nitrogen content in the final product was also high (5.6%, dry basis). In conclusion, the recycling of hair wastes produced in the leather manufacturing industry using the composting technology is feasible and a valuable organic fertilizer may be obtained

Co-composting of hair waste from the tanning industry with de-inking and municipal wastewater sludges

Production of waste hair in the leather manufacturing industry is increasing every year due to the adoption of hair-save unhairing techniques, leaving the tanners with the problem of coping with yet another solid by-product. Numerous potential strategies for hair utilisation have been proposed. However, the use of hair waste as agricultural fertiliser is one of its most promising applications due to the high nitrogen content of hair. Agricultural value of hair can be increased by composting. This paper deals with the composting of hair from the unhairing of bovine hide. Results indicated that hair cannot be either composted on its own or co-composted with de-inking sludge, a chemical complementary co-substrate. However, good results were obtained when co-composted with raw sludge from a municipal wastewater treatment plant at hair:raw sludge weight ratios 1:1, 1:2 and, 1:4 in lab scale and pilot plant scale composters. In all cases, a more stable product was achieved at the end of the process. Composting in the pilot plant composter was effectively monitored using Static Respiration Indices determined at process temperature at sampling (SRI(T)) and at 37 degrees C (SRI(37)). Notably, SRI(T) values were more sensitive to changes in the biological activity. In contrast, Respiratory Quotient (RQ) values were not adequate to follow the development of the process

Estudi de les emisions i la biofiltració dels gasos emesos en el procés de compostatge de diferents residus orgànics /

Consultable des del TDXTítol obtingut de la portada digitalitzadaEls processos de compostatge estan sovint relacionats amb la generació de males olors degut a les emissions de compostos nitrogenats, principalment amoníac, de compostos sulfurosos, i de compostos orgànics volàtils (COVs). Actualment, un procés de compostatge modern cal que es disseny i operi de manera que minimitzi les emissions i tracti eficaçment els gasos i olors generats. En aquest sentit, la biofiltració és una alternativa simple, econòmica i eficient a l'hora de reduir les emissions oloroses originades en processos de tractament de residus. L'objectiu d'aquesta tesi és l'estudi de les emissions d'amoníac i de COVs, així com la seva posterior biofiltració en processos de compostatge de residus orgànics de composició i propietats diferents (fracció orgànica de residus municipals (FORM), fangs d'estació depuradora d'aigües residuals digerits anaeròbiament i sense digerir, residus carnis i residus de pèl). A la vegada, s'ha dissenyat i construït un aparell per caracteritzar el comportament d'un suport orgànic de rebliment per biofiltrar amoníac en termes de degradació biològica, capacitat d'adsorció i capacitat d'absorció d'amoníac. Els resultats han mostrat com la quantitat d'amoníac volatilitzada en tots el processos de compostatge estudiats està directament influenciada per la relació C/N de la mescla a compostar. A la vegada, s'ha observat que les emissions d'amoníac augmenten exponencialment durant la fase termòfila del procés de compostatge, mentre que durant la fase final les emissions i la temperatura semblen estar relacionades de manera lineal. En el cas de l'estudi de les emissions de COVs, les màximes concentracions s'han detectat durant les primeres 48 hores de procés i s'ha apreciat un augment de les emissions a l'afegir una major quantitat d'estructurant a la mescla inicial a compostar. En el l'estudi de la biofiltració de les emissions d'amoníac s'ha constatat que la biofiltració emprant compost com a medi de rebliment elimina gran part de les emissions d'amoníac derivades del compostaje de FORM i fangs digerits amb eficàcies superiors al 95%. No obstant, s'ha observat una eliminació parcial de l'amoníac durant el compostaje de residus carnis degut a les elevades concentracions d'amoníac emeses i a possibles fenòmens d'inhibició de l'activitat biològica del biofiltre. Pel que fa a la biofiltració de COVs originats en processos de compostatge, s'ha observat que aquesta és altament dependent de la composició de la mescla de COVs volatilitzada i per tant assoleix diferents eficàcies d'eliminació en funció del residu a compostar, obtenint-se les majors eficàcies durant el compostatge de fangs frescos. S'ha constatat que el propi compost com a material de rebliment emet COVs en una concentració aproximadament de 50 mg C·m-3. Finalment, en l'estudi dels mecanismes de biofiltració d'amoníac, s'han considerat adequats els models de Freundlich i de Langmuir per descriure els equilibris dels processos d'adsorció d'amoníac dels materials de rebliment estudiats. S'ha observat que l'absorció d'amoníac es pot representar mitjançant el model lineal regit per la llei de Henry, amb valors de la constant de partició significativament superiors a la constant de Henry quan l'amoníac es dissol en aigua pura, i s'ha comprovat que l'absorció té un pes important com a mecanisme d'eliminació d'amoníac en el rang d'humitat òptim dels biofiltres. Finalment, les velocitats de biodegradació d'amoníac obtingudes han estat considerablement baixes si es comparen amb les dels mecanismes fisicoquímics d'eliminació d'amoníac. Aquest manifesta la importància de controlar les càrregues d'amoníac subministrades als biofiltres que operen en plantes de compostatge, per exemple mitjançant un pretractament emprant un rentador àcid, si es vol garantir un funcionament adequat del sistema a llarg termini.Composting processes are frequently related to bad odours generation due to the emissions of nitrogen compounds, mainly ammonia, sulphur compounds and volatile organic compounds (VOCs). Currently, modern composting processes have to be designed and operated minimising emissions and treating gases and odours efficiently. In this sense, biofiltration can be adapted to reduce emissions from composting processes. It is also considered a suitable technology in terms of waste recycling, emission reduction and low construction and operating costs. The aim of this thesis is the study of ammonia and VOCs emissions generated during the composting of different organic wastes (organic fraction of municipal solid wastes (OFMSW)), raw sludge, anaerobically digested sludge, animal by-products and hydrolysed hair). The abatement of the ammonia and VOCs generated during the waste composting using the biofiltration technology is also studied. Moreover, a new specific apparatus to characterise organic support media in terms of ammonia biological degradation, adsorption and absorption capacity, has been designed and constructed. Results have shown that the total amount of ammonia emitted during the composting process was directly related to the C/N ratio. Ammonia emissions revealed a strong dependence on temperature, with a distinct pattern in the thermophilic first stage of composting than that of the mesophilic final stage. VOCs emissions were higher during the beginning of the composting process. Biofiltration technology using compost as a biofilter media can effectively remove most of the ammonia content from the composting process of OFMSW and digested sludge, achieving removal efficiencies over 95%. However, in the case of animal by-products, only a partial removal of ammonia was obtained due to the high ammonia emissions. VOCs biofiltration from exhausted gases of composting processes can be performed achieving different efficiencies depending on the waste composted. More sustained removal efficiencies were obtained in the composting of raw sludge. Compost biofilters are emitters of VOCs themselves. Approximately basal emission of 50 mg C·m-3 was measured. Regarding the ammonia biofiltration mechanisms study, adsorption data were successfully fitted to Langmuir and Freundlich isotherms. The results also show that absorption could be represented by a Henry's law linear equation, with values of the Henry coefficient higher than that of pure water. Finally, ammonia biodegradation rates are considerably lower than absorption and adsorption rates. This fact shows the importance of controlling ammonia loading rates supplied to biofilters in composting plants in order to achieve a high efficiency in long term operation